Invasive sensors for determining the concentration of various analytes in body fluids, particularly the concentration of gasses such as oxygen and carbon dioxide in blood, have been proposed in the art.
U.S. Pat. No. 3,905,888 discloses an electrochemical sensor for determining the oxygen partial pressure in a biological medium comprising a flexible plastic tube which is permeable to oxygen and houses a pair of electrodes surrounded by an electrolyte.
Sensors for the determination of pH and pCO.sub.2 normally comprise one or more optical fibers in association with a suitable indicator for the parameter under investigation.
U.S. Pat. No. 4,200,110 discloses a fiber optic probe which includes an ion permeable membrane envelope which encloses the end of a pair of optical fibers. The operation of the probe depends upon the optical detection of a change in color of a pH sensitive dye. U.S. Pat. No. 4,943,364 discloses a fiber-optic probe for measuring the partial pressure of carbon dioxide in a medium comprising a hydrolyzed dye/gel polymer in contact with a bicarbonate solution enveloped in a membrane covering the distal end of the fiber.
U.S. Reissue Pat. No. 31,879 discloses a method for measuring the concentration of an analyte in a sample which involves measuring a change in the color characterization of a fluorescent indicator attached to an optical fiber, without or with a gas-permeable membrane.
Commonly assigned U.S. Pat. No. 4,889,407 discloses an optical waveguide sensor for determining an analyte in a medium, which sensor comprises an optical waveguide having a plurality of cells arranged in an array which substantially covers the cross-sectional area of the waveguide, each of said cells containing an indicator sensitive to said analyte.
When a probe, such as one of those disclosed in the above prior art, is used invasively, it is usually introduced into a body lumen, for example a blood vessel, with the aid of an introducer and, to protect the probe itself, avoid contamination, maintain sterility and also facilitate introduction, the probe is usually accommodated within an elongated tubular catheter.
The prior art patents mentioned above disclose sensors adapted to determine a single analyte. However, there is a need in the art for a single device which is capable of determining and monitoring a number of blood parameters, for example, pH, pO.sub.2, pCO.sub.2 and temperature, and which has a small enough diameter to be inserted into a blood vessel.
U.S. Pat. No. 4,727,730 discloses a blood pressure monitoring apparatus comprising a single fiber probe that interrogates three dye wells each using a fluorescent dye. Blood pressure is monitored with the aid of a diffraction grating.
U.S. Pat. No. 4,854,321 discloses a single probe having multiple dye wells for monitoring blood gases.
U.S. Pat. No. 4,279,795 discloses a hydrophilic-hydrophobic graft copolymer formed by the copolymerization of a free radical polymerizable vinyl monomer capable of forming a hydrophilic polymer and a hydrophobic macromolecular compound.
By using a biphasic membrane as described and claimed herein, it is possible to incorporate sensors for the determination and monitoring of pH, pO.sub.2, pCO.sub.2 and temperature in a single multi parameter catheter which is narrow enough to be inserted safely into a patient's blood vessel.
Since it is important to avoid contamination and direct operator contact when introducing the catheter into a patient's blood vessel, the invention also provides a device, or introducer, for said introduction.
U.S. Pat. No. 4,906,232 discloses an intravascular delivery device comprising seal means, a delivery assembly having an inner sleeve and stop means.
U.S. Pat. No. 4,960,412 discloses a valve assembly for a catheter introducer.
It has now been found that optimum results are obtained from a multi-parameter catheter if at least part of the tubular wall or outer sheath of the catheter is made from a biphasic membrane as disclosed herein.